The New Gravitational wave Observatory (NGO) is a space mission designed to measure gravitational radiation over a broad band at low frequencies, from about 100 µHz to 1 Hz, a band where the Universe is richly populated by strong sources of gravitational waves. (For a more detailed introduction to gravitational waves and how they are detected, please see the article on Gravitational waves - linked in the right-hand menu.)
NGO will measure signals from a wide range of different sources that are of strong interest to the astrophysics of black hole and galaxy formation, and also to tests of general relativity and to cosmology: massive black holes merging in galaxies at all distances; massive black holes consuming smaller compact objects; known binary compact stars and stellar remnants; members of known populations of more distant binaries; and probably other sources, possibly including relics of the extremely early Big Bang, which are as yet unknown.
These strong signals convey detailed information addressing scientific questions raised by ESA’s Cosmic Vision programme, such as "What are the fundamental laws of the Universe?" and "How did the Universe originate and what is it made of?"
The science objectives for NGO are as follows:
- Survey compact stellar-mass binaries and study the structure of the Galaxy:
- Elucidate the formation and evolution of Galactic stellar-mass compact binaries and thus constrain the outcome of the common envelope phase and the progenitors of (type Ia) supernovae;
- Determine the spatial distribution of stellar-mass binaries in the Milky Way;
- Improve our understanding of white dwarfs, their masses and their interactions in binaries, and enable combined gravitational and electromagnetic observations;
- Trace the formation, growth and merger history of massive black holes:
- Trace the formation, growth and merger history of massive black holes with masses from 105 to 107 solar masses during the epoch of growth of quasi-stellar objects and widespread star formation in the redshift range 0 < z < 5, through their coalescence in galactic halos;
- Capture the signal of coalescing massive black hole binaries with masses from 2 × 104 to 105 solar masses in the redshift range 5 < z < 10 when the Universe was less than one billion years old.
- Explore stellar populations and dynamics in galactic nuclei:
- Characterise the immediate environment of massive black holes in galactic nuclei with redshift z < 0.7 from extreme mass ratio capture signals;
- Discover intermediate-mass black holes from their captures by massive black holes;
- Confront General Relativity with observations:
- Detect gravitational waves directly and measure their properties precisely;
- Test whether the central massive objects in galactic nuclei are consistent with the Kerr black holes of General Relativity;
- Perform precision tests of dynamic strong-field gravity;
- Probe new physics and cosmology with gravitational waves:
- Measure the spectrum of cosmological backgrounds, or set upper limits on them, in the 10-4 Hz to 10-1 Hz band;
- Search for gravitational wave bursts from cosmic string cusps and kinks.
(For more detailed information about the NGO scientific objectives, please consult the NGO assessment study report (Yellow Book) - see link in right-hand menu.)